[NO ISSUE][STO] Fix write rate limiter calculation

[NO ISSUE][STO] Fix write rate limiter calculation

- user model changes: no
- storage format changes: no
- interface changes: no

Details:

- Fix the write request size to the write rate limiter
  by considering the page size.

Change-Id: If875755d65476339b90adcf6e654e32e97655f3d
Reviewed-on: https://asterix-gerrit.ics.uci.edu/c/asterixdb/+/15286
Integration-Tests: Jenkins <jenkins@fulliautomatix.ics.uci.edu>
Tested-by: Murtadha Hubail <mhubail@apache.org>
Reviewed-by: Murtadha Hubail <mhubail@apache.org>
Reviewed-by: Ali Alsuliman <ali.al.solaiman@gmail.com>